The invention concerns a tube-filling machine comprising a conveyer device for transporting a tube through different processing stations, wherein the processing stations comprise a filling station in which a filling pipe can be inserted from above into the substantially vertical tube and through which a filling medium can be introduced into the tube via a dosing means.
A known tube-filling machine comprises a conveyer device which is usually an endless loop or chain and which has a plurality of receptacles for one tube each. The empty tubes are inserted into the receptacles of the conveyer device in a feed station and are transported through several workstations, in particular a filling station and a subsequent sealing station. In the filling station, the tubes are filled via a filling pipe which is connected to a filling medium storage via a dosing means. The filling process should only be carried out when a tube has actually been received in the respective receptacle. Towards this end, a sensory presence check is carried out directly after the feed station to determine whether or not a tube is actually located in the examined receptacle. If this is not the case, the filling process for this receptacle is stopped.
Moreover, immediately after the feed station, the orientation or rotational position of the tube is compared with a predetermined desired position and is optionally corrected. The tube must be disposed in the correct rotational position to seal the tube with the correct orientation.
Empty plastic tubes are usually eccentric, i.e. their cross-sectional shape differs more or less from an ideal circular cross-section. Conventionally, before the filling station, the tubes are checked for eccentricity and tubes which differ greatly from the desired shape are discarded. The eccentricity check is very demanding and also unreliable.
Only when all mentioned checks, i.e. presence check, orientation check and eccentricity check have been satisfactorily carried out, is the tube released for filling in the filling station. In this fashion, missing tubes and strongly deformed tubes can be reliably detected. However, slightly damaged or deformed tubes which are not discarded in the above mentioned checks often cause problems in the filling station.
In the filling station, a relative motion obtains between the vertical tube, with open upper end, and a downwardly projecting vertical filling pipe to introduce the filling pipe into the tube. The filling pipe is usually fixed in place and the tube is lifted. When the tubes have been previously damaged, the lower end of the filling pipe might not be inserted into the tube but can be lowered onto the tube wall thereby compressing or even crushing the tube during further relative motion. If the dosing means is then activated, the filling medium is not filled into the tube but is discharged into the tube-filling machine, thereby requiring cleaning at great expense.
The same problems occur when an empty tube is removed from a receptacle after the presence check or drops down to thereby cause discharge of the filing medium into the filling station, despite the missing tube.
With tubes which are intrinsically bent or which have been previously seriously damaged, the filling pipe might not be inserted into the tube, rather may come to rest beside the tube such that, in the subsequent xe2x80x9cfilling processxe2x80x9d, the filling medium is also spilled into the tube-filling machine.
It is therefore the underlying purpose of the present invention to produce a tube-filling machine of the mentioned type with which the filling medium is introduced into the tubes with high reliability such that soiling of the tube-filling machine through defective filling is avoided.
This object is achieved in accordance with a tube filling machine of the above mentioned type in that a sensor device for detecting the relative position between the tube and the inserted filling pipe is disposed in the filling station, a control device is provided which receives a position signal from the sensor device and the dosing means can be controlled by means of the control device in dependence on the position signal.
In accordance with the invention, correct insertion of the filling pipe into the tube is checked directly in the filling station immediately before the start of the filling process. Only when correct insertion has been detected, is the filling process enabled and triggered by the control device. In this fashion, one can ensure that, in case of defective, crushed or missing tubes, no filling medium is discharged via the dosing means to reliably prevent any associated soiling of the tube-filling machine. This also advantageously avoids the stoppage of the tube-filling machine which would be required for cleaning.
In a preferred embodiment of the invention, the filling pipe and the sensor device are fixed to a frame and the relative motion is produced by lifting the tube in the filling station until the filling pipe is inserted into the tube. The sensor device can be adjusted in a direction parallel to the direction of the relative motion between the tube and the filling pipe for accommodating it to different tube shapes. In particular, the sensor device can be detachably disposed on a vertical rail for displacement along that rail.
Should the sensor device determine that either there is no tube or that the filling pipe is not correctly inserted into the tube, the dosing means is not triggered by the control device. Since operation of the tube filling machine produces a rapid sequence of switching on and off of the dosing means, a further development of the invention provides that the dosing means and in particular the dosing piston is driven by a servomotor which is switched on or off by the control device in dependence on the position signal. The use of a servomotor is advantageous since, in this event, all drive elements of the dosing drive and with the dosing piston are only in motion during the actual dosing process. All drive elements for the dosing piston are at rest immediately prior to the beginning of the dosing process. The above-mentioned sensor request is preferably effected immediately before the planned start of the dosing process. Prompt interruption is easily possible in this phase. Even if the sensor request should be carried out simultaneously with or directly after the start of the dosing process, the filling or dosing process can be aborted in the early phase due to the small inertia of the dosing drive of the filling or dosing process. This reliably prevents trailing of the dosing means and therefore discharge of the filling medium at an undesired point in time.
The sensor device must determine whether a tube is present and must check whether the filling pipe is correctly immersed into the tube. In an embodiment of the invention, the sensor device comprises an optical sensor and a light source which directs a beam of light onto the outer surface of the filling pipe. The light source and the sensor can thereby be disposed in a common housing. When the tube is lifted during insertion of the filling pipe, it enters the path of rays of this beam such that it no longer directly impinges on the outer surface of the filling pipe. This change in optical condition is detected and correspondingly evaluated by the control device. The optical sensor thereby detects, in particular, the reflected beam of light.
One single light source is normally sufficient for directing a single beam onto the filling pipe. However, in a further development of the invention, several beams are directed onto the filling pipe from different directions and are evaluated to ensure that the tube completely surrounds the filling pipe.
Further details and features of the invention can be extracted from the following description of an embodiment with reference to the drawing.